Comparison of haemolytic activity between Fusobacterium necrophorum subsp necrophorum and Fusobacterium necrophorum subsp. funduliforme in vitro and in vivo

Haemolytic activity of two subspecies of Fusobacterium necrophorum was compared in vitro and in who. F, necrophorum subsp. necrophorum (Fnn) showed a stronger activity than F. necrophorum subsp. funduliforme (Fnf) in vitro. Haemolytic activity of Fm and Fnf was 57.97%+/-1.90 and 17.33%+/-1.44, respectively, compared to complete haemolysis by distilled water. In the mice injected with Fnn, haemolysin was detected in the liver at a titre of from 1 : 16 to 1 : 128, and Fnn was recovered from all mice at a viable bacterial count of 10(5) to 10(6) cells per gram liver tissue. In the mice injected with Fnf, haemolysin titre was <1:2 to 1:32. No liver abscess was formed. The viable count of recovered bacteria was 10(3) to 10(5) cells per gram, except for two mice in which no Fnf was detected. The results suggest that haemolysin might be a virulence factor in this species.